Additive Manufacturing (AM) is generally a process in which three-dimensional (3D) objects are manufactured utilizing a computer model of the objects. These processes are used in various fields, such as design related fields for purposes of visualization, demonstration and mechanical prototyping, as well as for rapid manufacturing (RM).
Various techniques of AM exist, one such technique, otherwise known as 3D inkjet printing, being performed by a layer by layer inkjet deposition of building materials. Depending on the building materials, the layers are then cured or solidified. The building materials may include modeling materials and support materials, which form the object and the temporary support constructions supporting the object as it is being built. In cases where objects include overhanging features or shapes, e.g. curved geometries, negative angles, voids, and so on, objects are typically constructed using adjacent support constructions, which are used during the printing and then subsequently removed in order to reveal the final shape of the fabricated object.
During the AM process, at least one material (“object material” or “modeling material”) is deposited to produce the desired object but frequently a second material (“support material” or “supporting material”) is used to provide support for specific areas of the object during building and assure adequate vertical placement of subsequent object layers. Both materials, i.e modeling material and supporting material might be initially liquid and are subsequently hardened to form the required layer shape. The hardening process may be performed by a variety of methods, such as UV curing, phase change, crystallization, drying, etc. In all cases, the support material is deposited in proximity of the modeling material enabling the formation of complex object geometries and filling of object voids.
In such cases, the removal of the support structure thus formed is liable to be difficult and time consuming, and may damage the formed object.
Examples of materials that can be used as supporting materials are phase change materials, e.g., wax. These, at an appropriately high temperature, melt and thus permit support removal in the liquid state. One of the drawbacks of the phase change is that the temperature required for melting the supporting material may also cause deformation of the model structure.
Soluble supporting materials are especially appropriate for supporting small parts, because large masses of soluble material may require a lengthy period of time for dissolving.
To diminish such problems, the fabricated object is often immersed in water or in a solvent that is capable of dissolving the support materials. In many cases, however, the cleaning process may involve hazardous materials, manual labor and/or special equipment requiring trained personnel, protective clothing and expensive waste disposal. In addition, the dissolving process is usually limited by diffusion kinetics and may require very long periods of time, especially when the support constructions are large and bulky.
When using currently available commercial print heads, such as ink-jet printing heads, the support material must have a relatively low viscosity (about 10-20 cPs) at the working temperature so it can be jetted. Further, the support material should harden rapidly in order to allow building of subsequent layers. Additionally, the support material must have sufficient mechanical strength for holding the model material in place and low distortion for avoiding geometrical defects.
Known methods for removal of support materials include mechanical impact (applied by a tool or water-jet), as well as dissolution in a solvent, with or without heating. The mechanical methods, however, are labor intensive and are unsuited for small intricate parts. Further, the known dissolution methods sometimes require the use of aggressive chemical solvents that require safety precautions in both use and disposal. Additionally, the use of high temperatures during support removal may be problematic since there are model materials that are temperature sensitive, such as waxes and certain flexible materials. Such methods for removal of support materials are especially problematic for use in the office environment, where ease-of-use, cleanliness and environmental safety are major considerations.
In light of the above, it would be highly advantageous to have a material for use in 3D inkjet printing, that can be removed quickly and preferably automatically, by dissolution in water, or a non-hazardous water solution, rather than in aggressive chemical solvents. For this purpose, it is important that the material composition itself be, for example, non-toxic and environmentally safe.
One such class of materials known in the art, which is highly soluble in water, includes glycol based polymers such as polyethylene glycol (PEG). However, although such polymers are available in grades that may have a high enough melting point, suitable for 3D ink-jetting, such grades are frequently too viscous, e.g. for ink jet, and solidify relatively slowly, and therefore, are not suitable for use directly as material for 3D inkjet printing purposes.
Therefore, it is the object of this invention to provide a composition for 3D inkjet printing, featuring a balance between water-solubility, melting temperature, viscosity and solidification speed.